Giorgio Vasari on the Concept of a "Renaissance" (1550)

I think that anyone who will take the trouble to consider the matter carefully will arrive at the same conclusion as I have, that art owes its origin to Nature herself, that this beautiful creation the world supplied the first model, while the original teacher was that divine intelligence which has not only made us superior to the other animals, but like God Himself, if I may venture to say it. In our time it has been seen, as I hope to show quite shortly, that simple children, roughly brought up in the wilderness, have begun to draw by themselves, impelled by their own natural genius, instructed solely by the example of these beautiful paintings and sculptures of Nature. Much more then it is probable that the first men, being less removed from their divine origin, were more perfect, possessing a brighter intelligence, and that with Nature as a guide, a pure intellect for master, and the lovely world as a model, they originated these noble arts, and by gradually improving them brought them at length, from small beginnings, to perfection. I do not deny that there must have been an originator, since I know quite well that there must have been a beginning at some time, due to some individual. . . . 

But we will now pass over these matters, which are too vague on account of their antiquity, and we will proceed to deal with clearer questions, namely, the rise of the arts to perfection, their decline and their restoration or rather renaissance, and here we stand on much firmer ground. The practice of the arts began late in Rome, if the first figures were, as reported, the image of Ceres made of the metal of the possessions of Spurius Cassius, who was condemned to death without remorse by his own father, because he was plotting to make himself king. But although the arts of painting and sculpture continued to flourish until the death of the last twelve Caesars, yet they did not maintain that perfection and excellence which had characterized them before, as we see by the buildings of the time under successive emperors. The arts declined steadily from day to day, until at length by a gradual process they entirely lost all perfection of design. Clear testimony to this is afforded by the works in sculpture and architecture produced in Rome in the time of Constantine. . . .

[Source: Giorgio Vasari, The Lives of the Painters, Sculptors, and Architects (New York: J. M. Dent & Sons, Ltd., 1927), pp. 5-6.]

There is an online selection from Vasari's, Lives of the Painters.